BEIJING (Reuters) - A human rights activist best known as "Super Vulgar Butcher" who rose to prominence by harnessing social media to mobilize public support admitted in a closed-door trial that his actions "violated the law", a Chinese court said on Monday.

Wu Gan, 44, was detained in May 2015 and charged with subverting the state.

Known for his distinctive bald pate and cutting humor, Wu combined cyber-activism with eye-catching street performance to draw attention to causes ranging from wrongful imprisonment to freedom of speech.

He worked in an investigative capacity for a law firm, helping it find and vet cases involving abuses of power.

In a brief statement published on its official Weibo account on Monday afternoon, the Tianjin No.2 Intermediate People's Court said it did not hold an open hearing because Wu's case impinged on "state secrets".

"The defendant Wu Gan recognized his behavior violated criminal law and constituted a crime," the court said, adding that his lawyers were allowed to "fully express" their defense arguments.

The court said a verdict would be handed down at an unspecified later date.

Politically sensitive cases such as Wu's almost always result in a guilty verdict from China's Communist Party-controlled judiciary.

Wu's lawyer, Ge Yongxi, said it was "inconvenient" to talk about the case when reached by telephone.

In a pre-trial statement that Wu managed to slip to his lawyers during a recent meeting, Wu said he knew he would "receive a heavy sentence" because of his "refusal to accept a state-designated lawyer, plead guilty, and make a televised confession for their propaganda purposes".

"My crime of subverting the communist regime is a great honor for me," he said in the statement, published online by his father on Aug. 9.

"A guilty verdict issued by a dictatorial regime is a golden glittering trophy awarded to warriors for liberty and democracy."

Wu was detained at the start of what is now referred to as the "709 Crackdown", named after the date of the biggest sweep on July 9, 2015, when hundreds of lawyers and activists were targeted for arrest, detention or questioning.

Wu is one of the last defendants to go on trial, more than two years on.

Most of the lawyers and activists have been released after serving short or suspended sentences, usually after recording televised "confessions", pleading guilty and expressing contrition in court.

Wu's supporters say his trial was delayed and only held behind closed doors because of his refusal to follow suit, while also scoffing at any suggestion he could have any state secrets in his possession.

"Wu Gan's trial is a cruel farce and it is inconceivable that he will receive a fair hearing in what is a politically motivated prosecution," said Patrick Poon, China researcher for Amnesty International.

"He is merely being punished for refusing to stop his innovative and legitimate campaigns for justice in China."